(A). Low equivalent series resistance (ESR) is an important characteristic for capacitors used to filter the DC output of a switching power supply. A filter capacitor with a low ESR will act to even out the output voltage variations.

For more info see Wikipedia: Equivalent series resistance (ESR)

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(D). Electrolytic capacitors are often used in power supply circuits to filter the rectified AC.

Electrolytic capacitors have the advantage of high capacitance in a small volume, so they are very useful in power supply circuits.

For more info see Wikipedia: Electrolytic capacitors

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Ceramic capacitors have the advantage over other types of capacitors in they provide good function at comparatively low cost.

Silly hint: Ceramic Capacitors are Cheap

For more info see: ceramic capacitors

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An advantage of electrolytic capacitors is that they have high capacitance for given volume.

These capacitors are often used in power supplies for AC voltage filtering.

They are polarized and must be placed in the circuit in the proper orientation, as reverse-voltages can cause catastrophic (explosive) failure. Bad electrolytic caps can swell and leak the electrolyte out the vent grooves notched in the top, appearing as a crusty substance. Also the electrolytic capacitors may have large variations in capacitance due to their method of manufacture.

For more info see: Electrolytic capacitors

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(A). Effective capacitance may be reduced by lead inductance in a capacitor used at VHF and above.

The inductance of the lead wire can create a small inductance in series with the capacitor. This usually doesn't cause a large effect at lower frequencies (HF and below). However, as the frequency increases to VHF or higher, the lead inductive reactance can effectively cancel out the reactance of the capacitor, causing a very significant decrease in the total capacitance or the capacitor. One solution is to use capacitors with very short leads for working with higher frequencies.

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(C). The resistance of a resistor will change depending on the resistor's temperature coefficient. Most resistors will increase in resistance with increases in temperature, in other words they have a positive correlation or positive coefficient between resistance and temperature.

For more info see Wikipedia: Resistors

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One reason not to use wire-wound resistors in an RF circuit is that the resistor's inductance could make the circuit performance unpredictable.

The construction of a wire wound resistor is VERY similar to that of an inductor. So in situations where extra inductance may be an issue (such as RF circuits), they are not a good component choice.

Silly Hint: Something that is Unpredictable is usually something you do NOT choose.

For more info see Wikipedia: Wire-wound resistors

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(B). A thermistor is a device having a specific change in resistance with temperature variations.

A thermistor is a special type of resistor, specifically designed to change in resistance value with increased temperature. In this way it can act as a temperature sensor, relating an increase in resistance to an increase in temperature.

Hint: Remember a thermistor is a RESISTOR, and RESISTANCE is the property changing with temperature. Answers (C) and (D) are not about resistors, and answer (A) is wrong because the thermistor is NOT RESISTANT to change, or it would be useless as a temperature sensor.

For more info see Wikipedia: Thermistor

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This question could be asking about a couple of things:

(1) What advantage does a toroid core provide as opposed to a straight core?

(2) What advantage does a ferrite core provide as opposed to a powdered iron core?

Based on the correct answer, it seems like it's only asking about toroid versus straight.

Toroids have become popular because the amount of magnetic flux that leaks outside of the core itself is low, which makes it more efficient and it radiates less electromagnetic interference.

Additionally, toroid cores are a closed loop. In a straight core the magnetic field has to go pretty far from one end to enter at the other. This means that the toroid will typically produce a larger inductance.

Finally, by varying the size and thickness and characteristics of the ferrite itself, you can optimize a ferrite toroid for different frequencies.

Silly Hint: the TOROIDAL inductor gives you the TOTAL package.

For more info see Wikipedia: Toroidal inductor

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(C). The winding axes or coils of solenoid inductors should be placed at right angles to minimize their mutual inductance. Because each solenoid has an associated magnetic field, it is important to use this arrangement to avoid these fields interacting with each other.

For more info see Wikipedia: Solenoid

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(B). Mutual inductance between two inductors should be minimized to reduce unwanted coupling between circuits. Otherwise, energy may be transferred from one inductor to another elsewhere in the circuit, where the excess voltage could cause distortion of the signal or damage to components.

For more info see Wikipedia: Inductance

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(D). The Filter choke is the inductor used to help smooth the DC ouput from the rectifier in a conventional power supply. The choke filter uses induction to reduce the variations of frequency in the electric current passing through, smoothing the DC output.

For more info see Wikipedia: Choke

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(B). One effect of inter-turn capacitance in an inductor, is that the inductor may become self resonant at some frequencies. The wire turns or windings can produce a parasitic inter-turn capacitance. When the inter-turn capacitance interacts with the induction, it can produce a self-resonant oscillating circuit.

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